The technology of fabricating semiconductor integrated circuits has advanced with regard to the number of transistors, capacitors and other electronic devices which can be fabricated on a single integrated circuit chip. This increasing level of integration has resulted in large part from a reduction in the minimum feature sizes of the integrated circuits and an increase in the number of layers and functionality which make up the integrated circuit. The manufacture of integrated circuit components having this reduced size and the need to reduce production steps has placed new demands on all aspects of their production including the removal of resists and related materials with chemical stripper solutions.
Semiconductor devices for semiconductor integrated circuits or liquid crystal displays are commonly produced by a process including the steps of coating a substrate with one or more layers of polymeric resist materials to provide a resist film; patterning the photosensitive resist film by exposure to light and subsequent development; etching exposed portions of the substrate using the patterned resist film as a mask to form minute circuits; and removing the resist film from the inorganic substrate. Alternatively, after forming minute circuits, the post etch residues can be ashed and the remaining resist residues removed from the substrate with a post etch residue remover.
Resist stripping compositions that include aromatic quaternary ammonium hydroxide such as benzyltrimethylammonium hydroxide (BTMAH), a solvent such as an alkylsulfoxide, a glycol and a corrosion inhibitor and non-ionic surfactant do not completely remove many dry-film resists from a wafer surface. Similarly, compositions which use pyrrolidone-based solvents such as N-methylpyrrolidone (NMP) exhibit the same drawback in that they have not achieved complete removal of many dry-film resists and have compatibility problems with the photoresists. In general, compositions which include a quaternary ammonium hydroxide as tetramethylammonium hydroxide (TMAH) in N-methylpyrrolidone are not compatible with cured polyimide layers on the wafer.
The Cu film is adhered to layers underneath typically comprising organic dielectric films using Ti or TiW. Commonly this film is removed also in a dilute acid bath, but may be removed using a high energy plasma process. In addition, it may be beneficial to use a high energy plasma process to remove some of the organic dielectric film for a variety of reasons, including to improve electrical isolation of the solder bumps and/or as part of a plasma dicing process.
During the high energy plasma-based process, it is common for photoresist residues to remain behind. Further, plasma-based decomposition products can remain as post etch residues. Finally, organic or organometallic and metal oxides vaporized from the plasma etching process can sublime onto, or be sputtered onto, or react in the vapor phase with each other and deposit onto, the top of the solder bumps or back onto any of the other features on the semiconductor wafer surface.
In wafer level packaging, solder bumps can be formed using an electroplating process. Electrical contact for the plating step is made using a continuous Cu film to distribute the current across a wafer that is patterned with a photoresist mask. Metal is plated onto the copper surface in open features. After plating, the photoresist mask is removed and the continuous Cu film is etched from around the plated metal using a dilute acid solution to electrically disconnect the solder bumps.
The challenge remains to find a solution which cleans post etch residues, that is, residues created or resulting from an etching process (e.g. an acid and/or plasma etching process) which can include organic materials such as post etch degradation or damaged polyimide, new metal oxides formed such as SnO, and organometallic degradation products created from the plasma etching process such as from etching the Ti layer and/or the Sn etch products (collectively the post etch residues).
It is also desirable that this solution not only clean and remove photoresist post etch residues, but also maintains compatibility with permanent wafer features, such as metals comprising the solder caps (e.g. SnAg) and the copper pillars. A solution which is incompatible with the wafer features can result in further undesirably etching these metal surfaces including the copper pillars and solder bumps, resulting in yield loss.
The solution also should remain stable as a solution during the cleaning process to avoid leaving behind residues. Although solid particulates can form as byproducts in the solution during the heating and cooling cycle or over time, the particulates should remain in solution and not precipitate out of solution. Any precipitate byproducts can remain as deposits on wafer surface and production equipment. Thus, the solution should be stable at elevated temperatures encountered during operation and when cooled back to room temperatures.
This application addresses a composition and a process for removing organic, organometallic, and metal oxides from semiconductor substrates that have their origin as photoresist residues and etching residues on wafer, solder bump walls, and the top surface of the solder bumps.